Control device for vehicle and control method of vehicle

ABSTRACT

A control device includes an electronic control unit configured to expand a first detection range at least in front of a host vehicle during execution of current first steering control, determine whether next first steering control is needed to be implemented and whether a relative direction of a next second object with respect to the host vehicle is the same as a relative direction of a first object with respect to the host vehicle when the second object is detected, and perform relaxation steering control based on a target value smaller in absolute value than a return target value after an end of the current first steering control when the implementation of the next first steering control is determined to be needed and the relative directions with respect to the host vehicle are determined to be the same between the second and the first object.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. application Ser. No.16/050,721 filed Jul. 31, 2018 (allowed), which is based on JapanesePatent Application No. 2017-167198 filed on Aug. 31, 2017. The entiredisclosures of the prior applications are considered part of thedisclosure of the accompanying continuation application, and are herebyincorporated by reference.

BACKGROUND 1. Technical Field

The disclosure relates to a control device for a vehicle and a controlmethod of a vehicle.

2. Description of Related Art

Japanese Unexamined Patent Application Publication No. 2015-155295 (JP2015-155295 A) discloses a vehicle control device that performs asteering control when a vehicle passes a pedestrian. The vehicle controldevice identifies the pedestrian close to the vehicle using anon-vehicle sensor. The vehicle control device calculates a collisionprobability with an identified pedestrian and compares the calculatedprobability with a threshold value. When the collision probability withthe pedestrian is higher than the threshold value, the vehicle controldevice sets a separation distance from the identified pedestrian withina current traveling lane. Steering control is control for adjusting aposition of the vehicle in the right and left direction (vehicle widthdirection) when the vehicle passes the identified pedestrian based onthe set separation distance. With the steering control as describedabove, it is possible for the vehicle to safely pass the identifiedpedestrian while the vehicle avoids the collision with the identifiedpedestrian.

SUMMARY

In the steering control described above, an adjustment for returning theposition of the vehicle in the right and left direction to the center ofthe current traveling lane is also performed after the passing of theidentified pedestrian ends. After the end of the steering control, thevehicle control device identifies a next pedestrian using the on-vehiclesensor. When a collision probability with the next pedestrian is higherthan the threshold value, the vehicle control device sets the separationdistance and adjusts the position of the vehicle in the right and leftdirection when the vehicle passes the next pedestrian. That is, nextsteering control is performed.

Here, an interval from the end of the previous steering control to thestart of the current steering control may be short. In this case, theprevious steering control and the current steering control are performedcontinuously. However, when a relative direction of a pedestrian alreadypassed with respect to the vehicle is the same as a relative directionof the pedestrian to be passed, the position adjustment of the vehiclein the right and left direction in both steering control is performed inthe same direction. Therefore, the vehicle moves in a zigzag manner dueto the continuous steering control, and the driver may feeluncomfortable.

In another case, the vehicle control device may not be able to identifya next pedestrian even though the driver is aware of the next pedestrianto be passed by the vehicle during execution of the current steeringcontrol. The case described above is caused by a fact that a range foridentifying the pedestrian in the vehicle control device is always setto be constant. In the case as described above, when the relativedirection of the pedestrian with respect to the vehicle during thepassing is the same as the relative direction of the next pedestrianwith respect to the vehicle, the position return adjustment describedabove is performed as part of the current steering control.Consequently, the operation of the position return adjustment may causethe driver to feel anxiety that the vehicle approaches the nextpedestrian.

The disclosure provides a control device for a vehicle and a controlmethod of a vehicle capable of further reducing a sense of discomfortfelt by a driver during execution of steering control in the controldevice and the control method that perform the steering control when thevehicle passes an obstacle that has a possibility of colliding with thevehicle while the vehicle avoids the collision with the obstacle.

A first aspect of the disclosure relates to a control device for avehicle. The vehicle includes steered wheels. The control deviceincludes an electronic control unit. The electronic control unit isconfigured to execute first steering control to avoid a collision with afirst object that has a possibility of colliding with a host vehicle.The electronic control unit is configured to execute second steeringcontrol following the first steering control. The second steeringcontrol is control to steer the steered wheels in a direction oppositeto a steering direction of the steered wheels by the first steeringcontrol. The electronic control unit is configured to set an avoidancetarget value and a return target value when the first object is detectedin a first detection range. The avoidance target value is a target valueof a control amount for steering the steered wheels in the firststeering control. The return target value is a target value of a controlamount for steering the steered wheels in the second steering control.The electronic control unit is configured to expand the first detectionrange at least in front of the host vehicle during execution of currentfirst steering control based on the avoidance target value. When asecond object is detected in the expanded first detection range duringthe execution of the current first steering control, the electroniccontrol unit is configured to determine whether a next first steeringcontrol to avoid a collision with the second object that has apossibility of colliding with the host vehicle is needed to beimplemented and whether a relative direction of the second object withrespect to the host vehicle is the same as a relative direction of thefirst object with respect to the host vehicle. The electronic controlunit is configured to perform relaxation steering control based on atarget value smaller in absolute value than the return target valueinstead of current second steering control based on the return targetvalue after an end of the current first steering control when theimplementation of the next first steering control is determined to beneeded and the relative directions with respect to the host vehicle aredetermined to be the same between the second object and the firstobject.

In the control device according to the first aspect of the disclosure,the electronic control unit may be configured to perform the relaxationsteering control before next second steering control following the nextfirst steering control is started.

In the control device according to the first aspect of the disclosure,the electronic control unit may be configured to set the first detectionrange in front of the host vehicle. The electronic control unit may beconfigured to set a second detection range behind the host vehicle at aposition obtained by rotating the first detection range by 180 degreesaround a center of the host vehicle during the execution of the firststeering control such that the electronic control unit detects aparallel traveling vehicles that travels behind the host vehicle in alane adjacent to a lane in which the host vehicle travels. Theelectronic control unit may be configured to determine whether theparallel traveling vehicle approaches the host vehicle during theexecution of the relaxation steering control and whether aninter-vehicle distance between the host vehicle and the paralleltraveling vehicle is shorter than a determination value when theparallel traveling vehicle is detected in the second detection rangeduring the execution of the current first steering control. Theelectronic control unit may be configured to perform the current secondsteering control after the end of the current first steering controlwhen the parallel traveling vehicle is determined to approach the hostvehicle during the execution of the relaxation steering control and theinter-vehicle distance between the host vehicle and the paralleltraveling vehicle is determined to be shorter than the determinationvalue.

In the control device according to the first aspect of the disclosure,the electronic control unit may be configured to, during the executionof the current first steering control, expand the first detection rangein a direction in front of the host vehicle and in a direction oppositeto a movement direction of the host vehicle in a right and leftdirection of the host vehicle in the current first steering control. Anexpansion width of the first detection range in the right and leftdirection may be equal to or larger than a movement distance of the hostvehicle in the right and left direction in the current first steeringcontrol.

In the control device according to the first aspect of the disclosure,the vehicle may include an external sensor, and the electronic controlunit may be configured to detect the first object and the second objectin the first detection range based on information acquired by theexternal sensor.

A second aspect of the disclosure relates to a control method of avehicle. The vehicle includes steered wheels and an electronic controlunit. The control method includes: executing, by the electronic controlunit, first steering control to avoid a collision with a first objectthat has a possibility of colliding with a host vehicle; executing, bythe electronic control unit, second steering control following the firststeering control; setting, by the electronic control unit, an avoidancetarget value and a return target value when the first object is detectedin a first detection range; expanding, by the electronic control unit,the first detection range at least in front of the host vehicle duringexecution of a current first steering control based on the avoidancetarget value; when a second object is detected in the expanded firstdetection range during the execution of the current first steeringcontrol, determining, by the electronic control unit, whether a nextfirst steering control to avoid a collision with the second object thathas a possibility of colliding with the host vehicle is needed to beimplemented and whether a relative direction of the second object withrespect to the host vehicle is the same as a relative direction of thefirst object with respect to the host vehicle; and performing, by theelectronic control unit, a relaxation steering control based on a targetvalue smaller in absolute value than the return target value instead ofa current second steering control based on the return target value afteran end of the current first steering control when the implementation ofthe next first steering control is determined to be needed and therelative directions with respect to the host vehicle are determined tobe the same between the second object and the first object. The secondsteering control is control to steer the steered wheels in a directionopposite to a steering direction of the steered wheels by the firststeering control. The avoidance is a target value of a control amountfor steering the steered wheels in the first steering control. Thereturn target value is a target value of a control amount for steeringthe steered wheels in the second steering control.

According to the first aspect of the disclosure, since the firstdetection range is expanded at least in front of the host vehicle duringthe execution of the current first steering control, an opportunity todetect the second object increases. It is predictable that the nextfirst steering control to cause the host vehicle to avoid in the samedirection as the current first steering control may be started as soonas the current second steering control is ended through thedetermination relating to the next first steering control and thedetermination relating to the relative direction with respect to thehost vehicle. Then, when the prediction as described above is made, therelaxation steering control is performed based on the target valuesmaller in the absolute value than the return target value after the endof the current first steering control. Accordingly, the steering controlin which the driver does not feel uncomfortable or anxiety is realizedafter the end of the current first steering control.

According to the first aspect of the disclosure, furthermore, thesteering control in which the driver does not feel uncomfortable oranxiety is realized before the start of the next second steering controlafter the end of the current first steering control.

According to the first aspect of the disclosure, furthermore, since asecond detection range is set, the parallel traveling vehicle thattravels in parallel behind the host vehicle can be detected. Thepossibility of continuing the steering control is predictable throughthe determination relating to the approach of the parallel travelingvehicle to the host vehicle during the execution of the relaxationsteering control and the determination relating to the inter-vehicledistance between the host vehicle and the parallel traveling vehicle.Then, when the prediction as described above is made, the current secondsteering control is exceptionally performed based on the return targetvalue after the end of the current first steering control. Accordingly,it is possible to restrain the driver from feeling anxiety due to thecontinuity of the relaxation steering control.

According to the first aspect of the disclosure, furthermore, the firstdetection range during the execution of the first steering control isexpanded in front of the host vehicle and in the right and leftdirection thereof. The expansion width in the right and left directionis equal to or larger than the movement distance of the host vehicle inthe right and left direction in the current first steering control.Therefore, an opportunity to recognize the second object in the samedirection as the relative direction of the first object with respect tothe host vehicle increases.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a block diagram for describing a configuration of a controldevice according to Embodiment 1 of the disclosure;

FIG. 2 is a diagram for describing a method of specifying an avoidancetrajectory;

FIG. 3 is a diagram for describing an operation example of a hostvehicle when steering control is selected as assistance control;

FIG. 4 is a diagram for describing an operation example of the hostvehicle when a next second object is recognized after an end of a returnsteering control;

FIG. 5 is a diagram for describing an example of the steering controlaccording to Embodiment 1 of the disclosure;

FIG. 6 is a flowchart for describing an example of an assistance controlprocessing routine implemented by a driving assistance ECU in Embodiment1 of the disclosure;

FIG. 7 is a flowchart for describing an example of the assistancecontrol processing routine implemented by the driving assistance ECU inEmbodiment 1 of the disclosure;

FIG. 8 is a flowchart for describing an example of the assistancecontrol processing routine implemented by the driving assistance ECU inEmbodiment 1 of the disclosure;

FIGS. 9(a)-(d) are diagrams for describing an example of steeringcontrol according to a modification example 1 of Embodiment 1 of thedisclosure;

FIG. 10 is a flowchart for describing an example of a processing routineimplemented by the driving assistance ECU for realizing the steeringcontrol according to the modification example 1 of Embodiment 1 of thedisclosure;

FIGS. 11(a)-11(d) are diagrams for describing steering control accordingto a modification example 2 of Embodiment 1 of the disclosure;

FIG. 12 is a flowchart for describing an example of a processing routineimplemented by the driving assistance ECU for realizing steering controlaccording to the modification example 2 of Embodiment 1 of thedisclosure;

FIG. 13 is a diagram for describing a problem of relaxation steeringcontrol according to Embodiment 1 of the disclosure;

FIG. 14 is a diagram for describing an example of steering controlaccording to Embodiment 2 of the disclosure; and

FIG. 15 is a flowchart for describing an example of a processing routineimplemented by the driving assistance ECU for realizing exceptionsteering control according to Embodiment 2 of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the disclosure will be described based ondrawings. The same reference numeral is assigned to a common element ineach drawing, and redundant description is omitted. The disclosure isnot limited to the following embodiments.

First, Embodiment 1 of the disclosure will be described with referenceto FIGS. 1 to 12 .

Configuration of Control Device

FIG. 1 is a block diagram for describing a configuration of a controldevice according to Embodiment 1. The control device according toEmbodiment 1 includes a driving assistance ECU 10, a brake ECU 20, asteering ECU 30, and a warning ECU 40. Each ECU includes a microcomputeras a main part and is connected so as to be transmittable and receivablemutually through a controller area network (CAN) (not illustrated). TheECU stands for an electronic control unit. In the specification, themicrocomputer includes a central processing unit (CPU) and a storagedevice such as a read only memory (ROM) and a random access memory(RAM), and the CPU executes an instruction (program) stored in the ROMto realize various functions. In the specification, a vehicle on whichthe control device is mounted is also referred to as “host vehicle”.

The driving assistance ECU 10 is connected to an external sensor 51, asteering torque sensor 52, a yaw rate sensor 53, a vehicle speed sensor54, and an acceleration sensor 55. The steering torque sensor 52, theyaw rate sensor 53, the vehicle speed sensor 54, and the accelerationsensor 55 are classified as internal sensors.

The external sensor 51 has a function of acquiring information relatingto at least a road in front of the host vehicle and a solid objectpresent around the road. The solid object represents, for example, amoving object such as a pedestrian, a bicycle, and a vehicle, and afixed object such as a utility pole, a tree, and a guardrail.

The external sensor 51 includes, for example, a radar sensor and acamera sensor. The radar sensor radiates, for example, a radio wave in amillimeter wave band (hereinafter, referred to as “millimeter wave”) tothe surroundings (including at least the front side) of the hostvehicle. When a solid object reflecting the millimeter wave is presentin a radiation range, the radar sensor calculates presence or absence ofthe solid object and a relative relationship (distance between the hostvehicle and the solid object, relative speed of the host vehicle withrespect to the solid object, and the like) between the host vehicle andthe solid object by the reflected wave from the solid object. The camerasensor includes, for example, a stereo camera. The camera sensor imagesright and left scenes in front of the vehicle and calculates the shapeof a road, the presence or absence of the solid object, the relativerelationship between the host vehicle and the solid object, and the likebased on the imaged right and left image data. The camera sensorrecognizes a lane marker (hereinafter, referred to as “white line”) suchas an outside line of a roadway, a center line of the roadway, and aboundary line between a traveling lane and a passing lane to calculatethe shape of the road and a positional relationship between the road andthe host vehicle.

Information acquired by the external sensor 51 is also referred to as“target information”. The external sensor 51 repeatedly transmits thetarget information to the driving assistance ECU 10 at a predeterminedperiod. The external sensor 51 may not include the radar sensor and thecamera sensor and may include, for example, only the camera sensor.Information of a navigation system can be used for information on theshape of the road on which the host vehicle travels and informationrepresenting the positional relationship between the road and the hostvehicle.

The steering torque sensor 52 detects steering torque that a driverinputs to steered wheels and transmits a detection signal of thesteering torque to the driving assistance ECU 10. The yaw rate sensor 53detects a yaw rate applied to the host vehicle and transmits a detectionsignal of the yaw rate to the driving assistance ECU 10. The vehiclespeed sensor 54 detects a traveling speed of the host vehicle(hereinafter, referred to as “vehicle speed”) and transmits a detectionsignal of the traveling speed to the driving assistance ECU 10. Theacceleration sensor 55 detects front-rear acceleration which isacceleration applied in the front-rear direction of the host vehicle andlateral acceleration which is acceleration applied in the right and leftdirection (vehicle width direction) of the host vehicle, and transmits adetection signal of the lateral acceleration to the driving assistanceECU 10. The vehicle speed sensor 54 may be a tire-wheel assembly speedsensor.

The brake ECU 20 is connected to a brake actuator 21. The brake actuator21 is provided in a hydraulic circuit between a master cylinder (notillustrated) that pressurizes hydraulic oil by stepping force on a brakepedal and friction brake mechanisms 22 provided on right, left, front,and rear tire-wheel assemblies. The friction brake mechanism 22 includesa brake disc 22 a fixed to the tire-wheel assembly and a brake caliper22 b fixed to a vehicle body. The friction brake mechanism 22 operates awheel cylinder embedded in the brake caliper 22 b by hydraulic pressureof the hydraulic oil supplied from the brake actuator 21 to press abrake pad against the brake disc 22 a and generates friction brakingforce.

The steering ECU 30 is a control device of an electric power steeringsystem and is connected to a motor driver 31. The motor driver 31 isconnected to a steering motor 32. The steering motor 32 is incorporatedin a steering mechanism (not illustrated), a rotor of the motor isrotated by electric power supplied from the motor driver 31, and rightand left steering tire-wheel assemblies are steered by the rotation ofthe rotor. In a normal time, the steering ECU 30 causes the steeringmotor 32 to generate steering assist torque corresponding to steeringtorque of the driver detected by the steering torque sensor 52. Adirection of the steering torque is identified by a sign (positive ornegative) of the steering torque. For example, the steering torqueacting in the right direction is represented as positive steeringtorque, and the steering torque acting in the left direction isrepresented as negative steering torque. When a steering control commandvalue (steering torque command value described below) transmitted fromthe driving assistance ECU 10 is received when the driver does notoperate a steering wheel, the steering motor 32 is driven and controlledaccording to the steering control command value to steer the steeringtire-wheel assemblies.

The warning ECU 40 is connected to a human machine interface (HMI) 41.The HMI 41 is sound output means such as a buzzer and a speaker, anddisplay means such as a head up display (HUD), a display of thenavigation system, and combination meter. The warning ECU 40 outputs awarning sound from the sound output means according to an alert commandfrom the driving assistance ECU 10 or displays a warning message, awarning lamp, and the like on the display means to notify the driver ofan operation situation of assistance control.

Configuration of Driving Assistance ECU

The driving assistance ECU 10 will be described. The driving assistanceECU 10 includes a host vehicle track determination unit 11, a solidobject detector 12, an object recognition unit (hereinafter, referred toas object recognition unit) 13 that determines an object with apossibility of a collision, an assistance control determination unit 14,a deceleration controller 15, a steering controller 16, and a detectionrange setting unit 17.

The host vehicle track determination unit 11 generates informationrelating to the road on which the host vehicle travels at apredetermined calculation cycle based on the target informationtransmitted from the external sensor 51. With a front end centerposition of the host vehicle as an origin point, the host vehicle trackdetermination unit 11 generates, for example, coordinate information(position information) on the ground, the solid object, and the whiteline using a coordinate system expanding in the right and leftdirection, and the front side from the origin point. As described above,the host vehicle track determination unit 11 grasps a shape of thetraveling lane of the host vehicle defined by right and left whitelines, a position and an orientation of the host vehicle within thetraveling lane, and a relative position of the solid object with respectto the host vehicle. The host vehicle track determination unit 11calculates a turning radius of the host vehicle based on the yaw ratedetected by the yaw rate sensor 53 and the vehicle speed detected by thevehicle speed sensor 54, and calculates a trajectory of the host vehiclebased on the turning radius.

The solid object detector 12 discriminates whether the solid object isthe moving object or a stationary object based on a change in a positionof the solid object present in a detection range set by the detectionrange setting unit 17. When the solid object is discriminated as themoving object, the solid object detector 12 calculates a trajectory ofthe solid object. For example, a movement speed of the solid object inthe front-rear direction (traveling direction of the host vehicle) canbe calculated from a relationship between the vehicle speed and therelative speed with respect to the solid object. A movement speed of thesolid object in the right and left direction can be calculated from achange amount of a distance between a lateral end position of the solidobject and the white line detected by the external sensor 51 and thelike. The solid object detector 12 calculates the trajectory of thesolid object based on the movement speeds of the solid object in thefront-rear direction, and the right and left direction. The solid objectdetector 12 may calculate the trajectory of the solid object based onthe calculated trajectory of the host vehicle and the distance betweenthe host vehicle and the solid object detected by the external sensor51.

The object recognition unit 13 performs determination relating to thepossibility (hereinafter, referred to as “collision possibility”) of thecollision of the host vehicle with the solid object of when the hostvehicle travels with maintaining a current traveling state based on theposition of the solid object and the trajectory of the host vehicle.When the solid object is the moving object, the object recognition unit13 calculates the trajectory of the solid object and performs thedetermination relating to the collision possibility based on thetrajectory of the solid object and the trajectory of the host vehicle.The object recognition unit 13 calculates a time to collision TTC whichis a prediction time before the host vehicle collides with the solidobject (remaining time before collision) by the following equation (1)based on a distance L₁ between the solid object and the host vehicle anda relative speed Vr₁ with the solid object.TTC=L ₁ /Vr ₁  (1)

When the time to collision TTC is equal to or less than a collisiondetermination value TTC₁ set in advance, the object recognition unit 13determines that the collision possibility is high. When the time tocollision TTC is longer than a collision determination value TTC₂(>TTC₁) set in advance, the object recognition unit 13 determines thatthere is no collision possibility. When the time to collision TTC isbetween the collision determination value TTC₁ and the collisiondetermination value TTC₂, the object recognition unit 13 determines thatthe collision possibility is low. When the collision possibility isdetermined to be high and the collision possibility is determined to below, the object recognition unit 13 recognizes the solid object as theobject. That is, when the time to collision TTC is equal to or less thanthe collision determination value TTC₂, the object recognition unit 13recognizes the solid object as the object.

The assistance control determination unit 14 determines the presence orabsence of the recognition of the object by the object recognition unit13. When the object is recognized, the assistance control determinationunit 14 selects the assistance control for avoiding the collision withthe object and sets a start timing and an end timing of the selectedassistance control. The assistance control includes deceleration controlfor decelerating the host vehicle by intervening in the drivingoperation of the driver and steering control for controlling thesteering torque of the host vehicle by intervening in the drivingoperation of the driver.

The selection of the assistance control can be performed, for example,based on a level of the collision possibility. Specifically, when thecollision possibility is high, the assistance control determination unit14 selects the deceleration control as the assistance control. When thecollision possibility is low, the assistance control determination unit14 selects the steering control as the assistance control. Theassistance control determination unit 14 can also select a combinationof the deceleration control and the steering control as the assistancecontrol regardless of the level of the collision possibility. A methodof setting the start timing and the end timing of the selectedassistance control will be described below.

When the start timing and the end timing of the deceleration control areset, the deceleration controller 15 calculates a target deceleration fordecelerating the host vehicle. For example, a case where the object isstopped is taken as an example. When a vehicle speed (=relative speed)at a current timing is V, a deceleration of the host vehicle is a, and atime until the host vehicle stops is t, a traveling distance X until thehost vehicle stops can be represented by the following equation (2).X=V·t+(½)·a·t ²  (2)

The time t until the host vehicle stops can be represented by thefollowing equation (3).t=−V/a  (3)

Accordingly, the deceleration a which is needed to stop the host vehicleat a traveling distance TD can be represented by the following equation(4) by substituting equation (3) into equation (2).a=−V ²/2TD  (4)

In order to stop the host vehicle at a distance β before the object, thetraveling distance TD may be set to a distance (L₁-β) which is obtainedby subtracting the distance β from the distance L₁ detected by theexternal sensor 51. When the object is moved, the deceleration a may becalculated using the relative speed with respect to the object.

The deceleration controller 15 sets the deceleration a calculated asdescribed above to the target deceleration. However, the decelerationthat can be generated in the host vehicle has a limit (for example,about −1 G). Therefore, when an absolute value of the calculated targetdeceleration is larger than an absolute value of an upper limit valueamax, the deceleration controller 15 sets the target deceleration to theupper limit value amax. The deceleration controller 15 transmits abraking command representing the target deceleration to the brake ECU20. As described above, the brake ECU 20 controls the brake actuator 21according to the target deceleration to generate the friction brakingforce in the tire-wheel assemblies. As described above, an automaticbrake is operated and the host vehicle decelerates.

When the start timing and the end timing of the steering control areset, the steering controller 16 calculates and specifies the avoidancetrajectory in which the host vehicle may take to avoid the collisionwith the object at a predetermined calculation cycle. FIG. 2 is adiagram for describing a method of specifying the avoidance trajectory.For example, when the host vehicle is assumed to travel within a currenttraveling lane with maintaining the current traveling state, thesteering controller 16 specifies a route A through which the hostvehicle is predicted to travel. When the host vehicle adds the maximumchange in lateral acceleration for the host vehicle to turn safelywithin the current traveling lane to current lateral acceleration, thesteering controller 16 specifies a route B through which the hostvehicle is predicted to travel.

The steering controller 16 obtains a route candidate when the lateralacceleration is changed by a constant amount in a traveling range fromthe route A to the route B. The steering controller 16 obtains a firsttrajectory that can safely avoid the collision with an object RS byturning of a host vehicle VC and where the lateral acceleration becomesthe smallest based on a degree of interference between the routecandidate and the object. The steering controller 16 obtains a secondtrajectory where the host vehicle VC can travel by the side of theobject RS while a distance between the host vehicle VC and a boundaryline TLL is maintained constantly. Then, the steering controller 16calculates and specifies a trajectory connecting the first trajectoryand the second trajectory as the avoidance trajectory.

The steering controller 16 specifies a return trajectory after the hostvehicle avoids the collision with the object at a predeterminedcalculation cycle. The return trajectory is a trajectory for returningthe position of the host vehicle in the right and left direction to thecenter of the current traveling lane (hereinafter, referred to as“return trajectory”). A first end of the return trajectory is positionedon an extension line of the avoidance trajectory, and a second end ofthe return trajectory is positioned at the center of the currenttraveling lane. The calculation and specification of the returntrajectory are performed in parallel with the calculation andspecification of the avoidance trajectory. The steering controller 16obtains and specifies the trajectory for returning the host vehicletraveling along the avoidance trajectory to the center of the currenttraveling lane with predetermined lateral acceleration as the returntrajectory.

The steering controller 16 calculates a target yaw rate for causing thehost vehicle to travel along the avoidance trajectory and the returntrajectory specified as described above. The steering controller 16calculates target steering torque that can obtain the target yaw ratebased on the target yaw rate. The steering controller 16 stores inadvance a map (not illustrated) in which the target steering torque thatincreases as a variation between the yaw rate detected by the yaw ratesensor 53 and the target yaw rate increases is set and calculates thetarget steering torque with reference to the map. The calculationdescribed above is performed at a predetermined calculation cycle.

When the target steering torque is calculated, the steering controller16 calculates target steering assist torque obtained by subtracting acurrent steering torque of the driver from the target steering torque.The steering controller 16 calculates a steering torque command valuethat increases toward the calculated target steering assist torque andtransmits the calculated steering torque command value to the steeringECU 30. However, the steering torque is restricted. Therefore, when thecalculated target steering assist torque (positive target steeringassist torque) is larger than an upper limit value Trmax, the steeringcontroller 16 sets the target steering assist torque to the upper limitvalue Trmax. When the calculated target steering assist torque (negativetarget steering assist torque) is smaller than a lower limit valueTrmin, the steering controller 16 sets the target steering assist torqueto the lower limit value Trmin. The steering ECU 30 controls a switchingelement of the motor driver 31 to control energization to the steeringmotor 32 such that the steering motor 32 generates steering torquehaving the magnitude of the steering torque command value according tothe steering torque command value. As described above, the steeringtire-wheel assemblies are autonomously steered, and the host vehicletravels along the avoidance trajectory and the return trajectory.

Hereinafter, for convenience of description, the steering control basedon the avoidance trajectory is referred to as “avoidance steeringcontrol” and the steering control based on the return trajectory isreferred to as “return steering control”. The avoidance steering controlis an example of a first steering control. The return steering controlis an example of a second steering control.

The assistance control determination unit 14 transmits the alert commandto the warning ECU 40 at a stage before the automatic brake is operatedor before the steering tire-wheel assemblies are autonomously steered.As described above, the warning ECU 40 rings the sound output means ordisplays a warning message, a warning lamp, and the like on the displaymeans to inform the driver of the operation situation of the assistancecontrol.

The detection range setting unit 17 sets the detection range to detectthe object. The detection range is defined by a longitudinal width and alateral width in front of the host vehicle along the current travelinglane. The longitudinal width is set to, for example, a value α·Vobtained by multiplying the vehicle speed V at the current timing by acoefficient α. The lateral width is set to, for example, a value W·γobtained by multiplying the vehicle width W of the host vehicle by acoefficient γ. The coefficients α and γ are set in advance according toa degree of safety needed for the host vehicle. The coefficient α islarger than the collision determination value TTC₂, and the coefficientγ is larger than one. The longitudinal width and the lateral width canbe set to fixed values.

Details of Assistance Control Determination Unit

Details of the assistance control determination unit 14 will bedescribed. As described already, when the object is recognized, theassistance control determination unit 14 selects at least one of thedeceleration control or the steering control as the assistance control.FIG. 3 is a diagram for describing an operation example of the hostvehicle when the steering control is selected as the assistance control.In the example illustrated in FIG. 3 , a first object RS₁ is recognizedin a detection range DR. A position of the first object RS₁ is outside aleft white line LL, and a relative direction of the first object RS₁with respect to the host vehicle VC is the left direction. In theexample illustrated in FIG. 3 , it is assumed that a possibility of thecollision of the host vehicle VC with the first object RS₁ is determinedto be low. At least the steering control is assumed to be selected asthe assistance control so as to cause the host vehicle VC to pass thefirst object RS₁ instead of stopping the host vehicle VC before thefirst object RS₁.

Here, when the start timing of the avoidance steering control is tooearly, the autonomous steering interferes with a steering wheeloperation of the driver. For example, there is a case where theautonomous steering is started ahead of the steering wheel operationdespite a situation where the driver is aware of presence of the firstobject RS₁ and attempts to operate the steering wheel when the firstobject RS₁ and the host vehicle VC come close to each other. In the casedescribed above, the driver may feel a sense of discomfort. In order toavoid the problem as described above, the assistance controldetermination unit 14 sets a timing when the host vehicle VC ispredicted to be close to the first object RS₁ to the start timing of theavoidance steering control. When the steering control is in combinationwith the deceleration control, the assistance control determination unit14 sets the start timing of the deceleration control to the same timingas the start timing of the avoidance steering control.

The assistance control determination unit 14 sets a timing when the hostvehicle VC is predicted to completely pass the first object RS₁ to theend timing of the avoidance steering control. The timing when the hostvehicle VC is predicted to completely pass the first object RS₁ iscalculated by adding an execution period TA of the avoidance steeringcontrol to the start timing of the avoidance steering control. Theexecution period TA can be represented by the following equation (5)using a distance L₂ between the first object RS₁ and the host vehicleVC, a longitudinal width WRS₁ of the first object RS₁, and a relativespeed Vr₂ with the first object RS₁ at the start timing of the avoidancesteering control.TA=(L ₂ +WRS ₁)/Vr ₂  (5)

The end timing of the avoidance steering control normally coincides withthe start timing of the return steering control. The end timing of theavoidance steering control normally coincides with a switching timingfrom the avoidance steering control to the return steering control. Whenthe steering control is in combination with the deceleration control,the end timing of the avoidance steering control coincides with the endtiming of the deceleration control.

Switching Timing from Avoidance Steering Control to Return SteeringControl

The discrimination of the solid object by the solid object detector 12and the determination relating to the collision possibility by theobject recognition unit 13 are performed at a predetermined calculationcycle. Therefore, a second object is newly recognized during a periodfrom the start timing to the end timing of the avoidance steeringcontrol, the assistance control determination unit 14 selects nextassistance control for avoiding the collision with the second object.That is, when the second object is not recognized during the executionof the avoidance steering control, the avoidance steering control isswitched to the return steering control at the end timing of theavoidance steering control.

When the second object is recognized during a period from the starttiming to the end timing of the return steering control or after an endof the return steering control, the assistance control determinationunit 14 selects the next assistance control. FIG. 4 is a diagram fordescribing an operation example of the host vehicle when the secondobject is recognized after the end of the return steering control. Inthe example illustrated in FIG. 4 , the steering control is alreadyimplemented as the assistance control for avoiding the collision withthe first object RS₁. In the example illustrated in FIG. 4 , a secondobject RS₂ is recognized in the detection range DR after the end of thesteering control. A position of the second object RS₂ is outside theleft white line LL, and a relative direction of the second object RS₂with respect to the host vehicle VC is the same left direction as therelative direction of the first object RS₁.

In the example illustrated in FIG. 4 , it is assumed that a possibilityof the collision of the host vehicle VC with the second object RS₂ isdetermined to be low. At least the steering control is assumed to beselected as the assistance control so as to cause the host vehicle VC topass the second object RS₂ instead of stopping the host vehicle VCbefore the second object RS₂. Consequently, next steering control isstarted as soon as current steering control is ended. That is, nextavoidance steering control to cause the host vehicle VC to avoid in thesame direction (right direction) as current avoidance steering controlis started immediately after the end of current return steering control.Therefore, the host vehicle VC moves in a zigzag manner.

The second object RS₂ recognized after the end of the current returnsteering control is not naturally recognized before an end of thecurrent avoidance steering control. Accordingly, when the driver isalready aware of the presence of the second object RS₂ before the end ofthe current avoidance steering control, the autonomous steering by thecurrent return steering control causes the driver to feel anxiety thatthe host vehicle VC approaches the second object RS₂.

Feature of Steering Control According to Embodiment 1

In Embodiment 1, the detection range set by the detection range settingunit 17 is expanded during the period from the start timing to the endtiming of the avoidance steering control. FIG. 5 is a diagram fordescribing an example of the steering control according to Embodiment 1.In the example illustrated in FIG. 5 , the detection range DR isexpanded in front of the host vehicle VC and in the left directionthereof along the current traveling lane. The longitudinal width of adetection range EDR after the expansion is set to, for example, a valueδ·α·V obtained by multiplying the value α·V of the longitudinal widthbefore the expansion by a coefficient δ. The lateral width of thedetection range EDR is set to, for example, a value W·γ+ε obtained byadding an expansion width ε in the left direction to the value W·γ ofthe lateral width before the expansion. The coefficient δ is larger thanone, and the expansion width ε is equal to or larger than a maximummovement distance MDmax of the host vehicle VC. The maximum movementdistance MDmax is the maximum value of a movement distance of the hostvehicle VC in the right direction (avoidance direction) by the avoidancesteering control.

In the example illustrated in FIG. 5 , a candidate RSC of the secondobject is detected in the detection range EDR. Therefore, the drivingassistance ECU 10 performs the same processing as the processing whenthe first object RS₁ is recognized with respect to the candidate RSC.However, the processing with respect to the candidate RSC is performedwith scheduled positions of the candidate RSC and the host vehicle VC atan end timing of the steering control (that is, end timing of returnsteering control) and a relative speed with the candidate RSC at the endtiming as the reference when the steering control for avoiding thecollision with the first object RS₁ is performed as scheduled, insteadof positions of the candidate RSC and the host vehicle VC at a timing ofdetecting the candidate RSC.

Specifically, the object recognition unit 13 predictively performsdetermination relating to a possibility of the collision of the hostvehicle VC with the candidate RSC after the steering control foravoiding the collision with the first object RS₁ is ended. First, theobject recognition unit 13 calculates the time to collision TTC beforethe host vehicle VC collides with the candidate RSC using the aboveequation (1). However, the distance L₁ of equation (1) is replaced witha distance between the candidate RSC and the host vehicle VC at the endtiming of the steering control. The relative speed Vr₁ of equation (1)is replaced with a relative speed with the candidate RSC at the endtiming of the steering control. The object recognition unit 13discriminates whether the candidate RSC corresponds to the second objectby comparing the collision determination values TTC₁, TTC₂ with thecalculated time to collision TTC.

In the example illustrated in FIG. 5 , the candidate RSC is assumed tobe recognized as a second object RS₃. In the case, the assistancecontrol determination unit 14 selects the assistance control and setsthe start timing and the end timing of the selected assistance controlin the same manner as when the first object RS₁ is recognized A positionof the second object RS₃ is outside the left white line LL, and arelative direction of the second object RS₃ with respect to the hostvehicle VC is the same direction (left direction) as the relativedirection of the first object RS₁. In the example illustrated in FIG. 5, it is assumed that a possibility of the collision of the host vehicleVC with the second object RS₃ is determined to be low after the end ofthe steering control for avoiding the collision with the first objectRS₁. At least the steering control is assumed to be selected as theassistance control so as to cause the host vehicle VC to pass the secondobject RS₃ instead of stopping the host vehicle VC before the secondobject RS₃.

As described above, when the steering control is selected as theassistance control, the next avoidance steering control to cause thehost vehicle VC to avoid in the same direction as the current avoidancesteering control is started as soon as the current return steeringcontrol is ended. The assistance control determination unit 14 cancelsthe start timing of the current return steering control. The assistancecontrol determination unit 14 cancels the start timing of the nextavoidance steering control. That is, the end timing of the currentavoidance steering control and the end timing of the next avoidancesteering control are valid. When the current steering control or thenext steering control is in combination with the deceleration control,the assistance control determination unit 14 does not cancel the endtiming of the deceleration control and cancels the start timing of thecurrent return steering control. That is, the end timing of thedeceleration control in combination with the current steering control orthe next steering control, the end timing of the current avoidancesteering control, and the end timing of the next avoidance steeringcontrol are valid.

When the start timing of the current return steering control iscanceled, the steering controller 16 specifies the shortest trajectoryconnecting the avoidance trajectory in the current steering control tothe return trajectory in the next steering control as a connectiontrajectory. The steering controller 16 calculates a target yaw rate forcausing the host vehicle VC to travel along the connection trajectoryspecified as described above and the return trajectory in the nextsteering control. The steering controller 16 calculates target steeringtorque that can obtain the target yaw rate based on the target yaw rate.An absolute value of the calculated target steering torque is smallerthan an absolute value of the target steering torque in the alreadycanceled current return steering control. When the target steeringtorque is calculated, the steering controller 16 calculates targetsteering assist torque obtained by subtracting a current steering torqueof the driver from the target steering torque. The steering controller16 calculates a steering torque command value that increases toward thecalculated target steering assist torque and transmits the calculatedsteering torque command value to the steering ECU 30.

Specific Processing in Embodiment 1

FIGS. 6 to 8 are flowcharts for describing examples of the assistancecontrol processing routines implemented by the driving assistance ECU 10in Embodiment 1. The processing routines are repeatedly implemented at apredetermined calculation cycle during a period while an ignition switchis on.

When the processing routines illustrated in FIGS. 6 to 8 are activated,the driving assistance ECU 10 first determines whether the object isrecognized (step S10). The recognition processing of the object is asdescribed in the description of the object recognition unit 13. When thedriving assistance ECU 10 determines that the object is not recognized,the driving assistance ECU 10 exits the processing routine.

In step S10, when the driving assistance ECU 10 determines that theobject is recognized, the driving assistance ECU 10 selects theassistance control (step S12) and sets at least one of the start timingor the end timing of the selected assistance control (step S14). Theselection processing of the assistance control and the settingprocessing such as the start timing of the selected assistance controlare as described in the description of the assistance controldetermination unit 14.

Following step S14, the driving assistance ECU 10 determines whether thesteering control is selected as the assistance control (step S16). Whenthe driving assistance ECU 10 determines that the steering control isnot selected as the assistance control, that is, the decelerationcontrol is selected, the driving assistance ECU 10 sets the targetdeceleration (step S18). The setting processing of the targetdeceleration is as described in the description of the decelerationcontroller 15. Then, the driving assistance ECU 10 transmits the brakingcommand to the brake ECU 20 such that the deceleration control startsfrom the start timing set in step S14 (step S20).

In step S16, when the driving assistance ECU 10 determines that thesteering control is selected as the assistance control, the drivingassistance ECU 10 sets the target steering assist torque (step S22). Thesetting processing of the target steering assist torque is as describedin the description of the steering controller 16. Then, the drivingassistance ECU 10 transmits the steering torque command value to thesteering ECU 30 such that the avoidance steering control starts from thestart timing set in step S14 (step S24). When the deceleration controlis in combination with the steering control, the target steering assisttorque and the target deceleration may be set in step S22 and thesteering torque command value and the braking command may be transmittedin step S24.

Following step S24, the driving assistance ECU 10 determines whether thestart timing of the avoidance steering control comes (step S26). Thedetermination processing in step S26 is repeated before a positivedetermination result is obtained. When the positive result is obtained,that is, when the driving assistance ECU 10 determines that the starttiming of the avoidance steering control comes, the driving assistanceECU 10 expands the detection range (step S28). The expansion processingof the detection range is as described in the description of FIG. 5 .

Following step S28, the driving assistance ECU 10 determines whether theend timing of the avoidance steering control comes (step S30). That is,the driving assistance ECU 10 determines whether the avoidance steeringcontrol is being executed. When the driving assistance ECU 10 determinesthat the end timing of the avoidance steering control comes, the drivingassistance ECU 10 reduces the detection range (step S32). That is, thedriving assistance ECU 10 returns the detection range expanded in stepS28 to the original range.

In step S30, when the driving assistance ECU 10 determines that the endtiming of the avoidance steering control does not come, the drivingassistance ECU 10 determines whether the second object is recognized(step S34). The recognition processing of the second object is asdescribed in the description of FIG. 5 . When the driving assistance ECU10 determines that the second object is not recognized, the drivingassistance ECU 10 returns to the determination processing in step S30.

In step S34, when the driving assistance ECU 10 determines that thesecond object is recognized, the driving assistance ECU 10 selects theassistance control (step S36) and sets at least one of the start timingor the end timing of the selected assistance control (step S38). Theselection processing of the assistance control and the settingprocessing such as the start timing of the selected assistance controlare as described in the description of FIG. 5 .

Following step S38, the driving assistance ECU 10 determines whether thesteering control is selected as the assistance control (step S40). Whenthe driving assistance ECU 10 determines that the steering control isnot selected as the assistance control, that is, the decelerationcontrol is selected, the driving assistance ECU 10 sets the targetdeceleration (step S42). The processing in step S42 is the same as theprocessing in step S18. Then, the driving assistance ECU 10 transmitsthe braking command to the brake ECU 20 such that the decelerationcontrol starts from the start timing set in step S38 (step S44).

In step S40, when the driving assistance ECU 10 determines that thesteering control is selected as the assistance control, the drivingassistance ECU 10 determines whether a relative direction (rightdirection or left direction) of the first object according to currentsteering control with respect to the host vehicle is the same as therelative direction of the second object recognized in step S34 withrespect to the host vehicle (step S46). When the relative directions areopposite to each other, determination can be made that there is a highpossibility that the next avoidance steering control is started in adirection opposite to the current avoidance steering control. Therefore,when the driving assistance ECU 10 determines that the relativedirections are opposite to each other, the driving assistance ECU 10proceeds to step S50.

When the relative directions are the same, determination can be madethat the next avoidance steering control to cause the host vehicle toavoid in the same direction as the current avoidance steering control isstarted. Therefore, in step S46, when the driving assistance ECU 10determines that the relative directions are the same, the drivingassistance ECU 10 transmits the cancel command for prohibiting theexecution of the return steering control in which the end timing of thecurrently executed avoidance steering control coincides with the starttiming of the next avoidance steering control to the steering ECU 30(step S48).

Following step S48, the driving assistance ECU 10 sets the targetsteering assist torque (step S50). The setting processing of the targetsteering assist torque is as described in the description of FIG. 5 .Then, the driving assistance ECU 10 transmits the steering torquecommand value to the steering ECU 30 (step S52) and returns to step S30.The steering torque command value transmitted in step S52 is the commandvalue for the host vehicle to travel along the connection trajectoryfrom the end timing of the currently executed avoidance steering controland to travel along a return trajectory from a start timing of nextreturn steering control.

With the control device according to Embodiment 1 described above, thefollowing effects can be obtained. That is, when the steering control isselected as the assistance control, the control device expands thedetection range during the execution of the avoidance steering controlin front of the host vehicle and in the relative direction of the firstobject with respect to the host vehicle. Therefore, an opportunity torecognize the second object in the same direction as the relativedirection of the first object with respect to the host vehicle can beincreased.

When the second object is recognized, the control device performsdetermination relating to a relative direction of the second object.Therefore, it is possible to predict that the next avoidance steeringcontrol to cause the host vehicle VC to avoid in the same direction ascurrent avoidance steering control may be started immediately after theend of the current return steering control. When the prediction asdescribed above is made, the control device can prohibit the executionof the current return steering control. Therefore, the vehicle moves ina zigzag manner.

Modification Example of Embodiment 1

When the avoidance directions of the current and next avoidance steeringcontrol are turned out to be the same direction, the control deviceaccording to Embodiment 1 cancels the end timing of the current returnsteering control and the start timing of the next avoidance steeringcontrol. Further, the control device specifies the connection trajectoryto calculate the target steering assist torque. However, the timingdescribed above may not be canceled, and the connection trajectory maynot be specified. The modification example as described above will bedescribed with reference to FIGS. 9 to 12 .

FIGS. 9(a)-9(d) are diagrams for describing an example of the steeringcontrol according to a modification example 1 of Embodiment 1. Theautonomous steering by the steering control according to Embodiment 1 isshown in FIGS. 9(a) and 9(b). In Embodiment 1, the execution of thecurrent return steering control and the next avoidance steering controlis prohibited, and the target steering assist torque is calculated byseparately specifying the connection trajectory. Therefore, inEmbodiment 1, the host vehicle VC travels along the connectiontrajectory from a point P₁ (that is, point where the host vehicle VC ispredicted to reach at the end timing of the current avoidance steeringcontrol) to a point P₂ (that is, point where the host vehicle VC ispredicted to reach at the start timing of the next return steeringcontrol).

The autonomous steering by the steering control according to themodification example 1 is shown in FIGS. 9(c) and 9(d). In modificationexample 1, the execution of the current return steering control and thenext avoidance steering control is not prohibited, and an upper limitvalue is set to the target steering torque (or change amount thereof) inthe current return steering control and the next avoidance steeringcontrol to calculate the target steering assist torque. Therefore,lateral acceleration of the host vehicle VC in the current returnsteering control and the next avoidance steering control becomes smallerthan the original lateral acceleration, and the host vehicle VC travelsalong gentle return trajectory and avoidance trajectory.

FIG. 10 is a flowchart for describing an example of a processing routineimplemented by the driving assistance ECU 10 for realizing the steeringcontrol according to the modification example 1 of Embodiment 1. Whenthe processing routine of FIG. 10 is replaced with the processingroutine illustrated in FIG. 8 , the assistance control processingroutine according to the modification example 1 is described. Theprocessing routine illustrated in FIG. 10 differs from the processingroutine illustrated in FIG. 8 in the processing when the positivedetermination result is obtained in step S46.

That is, when the positive determination result is obtained, the drivingassistance ECU 10 transmits the cancel command for prohibitingemployment of the target steering assist torque in the current returnsteering control to the steering ECU 30 (step S54). The drivingassistance ECU 10 calculates the target steering assist torque under acondition that an upper limit value TTrmax is set to the target steeringtorque (step S56). Then, the driving assistance ECU 10 transmits thesteering torque command value to the steering ECU 30 (step S58) andreturns to step S30. The steering torque command value transmitted instep S58 is the command value for the host vehicle to travel along thegentle trajectories described above from the end timing of the currentlyexecuted avoidance steering control and the start timing of the nextavoidance steering control, and to travel along the normal returntrajectory from the start timing of the next return steering control.

FIGS. 11(a)-(d) are diagrams for describing steering control accordingto a modification example 2 of Embodiment 1. The autonomous steering bythe steering control according to Embodiment 1 is shown in FIGS. 11(a)and 11(b). As described in FIGS. 9(a) and 9(b), in Embodiment 1, thehost vehicle VC travels along the connection trajectory from the pointP₁ to the point P₂.

The autonomous steering by the steering control according to themodification example 2 is shown in FIGS. 11(c) and (d). In themodification example 2, only the execution of the current returnsteering control is prohibited, and the end timing of the currentavoidance steering control is extended. Therefore, the point where thehost vehicle VC is predicted to reach shifts from the point P₁ to thepoint P₃ at the end timing of the current avoidance steering control.Consequently, the host vehicle VC travels along the second trajectoryfrom the point P₁ to the point P₃ and travels along the avoidancetrajectory connected to the second trajectory from the start timing ofthe next avoidance steering control.

FIG. 12 is a flowchart for describing an example of a processing routineimplemented by the driving assistance ECU 10 for realizing steeringcontrol according to a modification example 2 of Embodiment 1. When theprocessing routine of FIG. 12 is replaced with the processing routineillustrated in FIG. 8 , the assistance control processing routineaccording to the modification example 2 is described. The processingroutine illustrated in FIG. 12 differs from the processing routineillustrated in FIG. 8 in the pieces of processing after step S48.

That is, following step S48, the driving assistance ECU 10 transmits anextension command to extend the end timing of the currently executedavoidance steering control to the steering ECU 30 (step S60). Anextension period is from the end timing before the change to the starttiming of the next avoidance steering control set in step S38. Thedriving assistance ECU 10 calculates the target steering assist torque(step S62). Then, the driving assistance ECU 10 transmits the steeringtorque command value to the steering ECU 30 (step S64) and returns tostep S30. The steering torque command value transmitted in step S62 isthe command value for the host vehicle travels along a current secondtrajectory until the end timing after the change, travels along theavoidance trajectory connected to the second trajectory from the starttiming of the next avoidance steering control, and travels along thenormal return trajectory from the start timing of the next returnsteering control.

The control device according to Embodiment 1 calculates the steeringtorque (target steering torque, target steering assist torque, andsteering torque command value) as a control amount for steering thesteering tire-wheel assemblies. However, the control device maycalculate a steering angle (target steering angle, target steeringassist angle, and steering angle command value) instead of the steeringtorque. In the case, for example, assuming that a steering angle neutralpoint is 0°, the steering angle when the steering tire-wheel assembliesare rotated in the right direction from the steering angle neutral pointcan be represented as a positive value, and the steering angle when thesteering tire-wheel assemblies are rotated in the left direction can berepresented as a negative value.

As described above, when it is predicted that the direction of avoidingthe collision with the second object is the same direction as theavoidance direction of the currently executed avoidance steeringcontrol, various modifications can be employed in embodiment 1 as longas control (hereinafter, referred to as “relaxation steering control”)which is an intermediate steering control connecting between thecurrently executed avoidance steering control and the next returnsteering control and reduces an absolute value of a target value of asteering control amount compared with the current return steeringcontrol and the next avoidance steering control is performed. Themodification can be similarly employed in Embodiment 2 of the disclosuredescribed next.

Embodiment 2 of will be described with reference to FIGS. 13 to 15 .Since a configuration of the control device according to Embodiment 2 iscommon to the configuration of Embodiment 1, the description of theconfiguration will be omitted.

Feature of Steering Control According to Embodiment 2

When it is predicted that the direction of avoiding the second object isthe same direction as the avoidance direction of the currently executedavoidance steering control, the control device according to Embodiment 1performs the relaxation steering control that reduces the absolute valueof the target steering assist torque than the original value. Thesteering control according to Embodiment 2 is exceptionally performedduring the execution of the relaxation steering control. Hereinafter,for convenience of description, the steering control according toEmbodiment 2 is referred to as “exception steering control”.

FIG. 13 is a diagram for describing a problem of the relaxation steeringcontrol according to Embodiment 1. In the example illustrated in FIG. 13, the relaxation steering control similar to the relaxation steeringcontrol described in FIG. 5 is performed. However, in the exampleillustrated in FIG. 13 unlike FIG. 5 , a host vehicle VC₁ travels on thetraveling lane and a parallel traveling vehicle VC₂ travels on thepassing lane in two lanes set by the boundary line TLL. The host vehicleVC approaches the boundary line TLL during the execution of therelaxation steering control. Therefore, when the parallel travelingvehicle VC₂ travels with maintaining a current traveling state and theparallel traveling vehicle VC₂ passes the host vehicle VC₁ before thehost vehicle VC₁ travels by a side of the second object RS₃, the driverof the host vehicle VC₁ may feel anxiety at the time of the passing.

In Embodiment 2, the detection range set by the detection range settingunit 17 is increased to two positions during the period from the starttiming to the end timing of the avoidance steering control. FIG. 14 is adiagram for describing an example of the steering control according toEmbodiment 2. In the example illustrated in FIG. 14 , the expandeddetection ranges are set in front of and behind the host vehicle VCalong the current traveling lane. A size of a front detection range EDRFis the same as the size of the detection range EDR described in FIG. 5 .The rear detection range EDRR is obtained by rotating the detectionrange EDRF by 180 degrees with the center of the host vehicle VC₁ as therotation center. A size of the detection range EDRR is the same as thesize of the detection range EDRF. The detection range EDR, the detectionrange EDRF are the examples of a first detection range. The detectionrange EDRR is a example of a second detection range.

In Embodiment 2, the assistance control determination unit 14 performsdetermination relating to a possibility of continuing the relaxationsteering control (hereinafter, referred to as “continuity possibility”)during the execution of the avoidance steering control. The assistancecontrol determination unit 14 calculates a catch-up timing when theparallel traveling vehicle VC₂ catches up with the host vehicle VC₁based on a distance L₃ between the host vehicle VC₁ and the paralleltraveling vehicle VC₂, and a relative speed Vr₃ with the paralleltraveling vehicle VC₂. The assistance control determination unit 14calculates an inter-vehicle distance when the parallel traveling vehicleVC₂ approaches closest to the host vehicle VC₁ during the execution ofthe relaxation steering control based on a trajectory of the paralleltraveling vehicle VC₂ and a connection trajectory.

Then, the assistance control determination unit 14 determines whetherthe parallel traveling vehicle VC₂ catches up with the host vehicle VC₁during the execution of the relaxation steering control based on thecatch-up timing. The assistance control determination unit 14 comparesthe inter-vehicle distance with a determination value LTH. The hostvehicle VC₁ and the parallel traveling vehicle VC₂ travel each travelinglane, and the parallel traveling vehicle VC₂ is not assumed to interferewith the host vehicle VC₁. Accordingly, the determination value LTH isset to a value having a relatively large margin. When the assistancecontrol determination unit 14 determines that the parallel travelingvehicle VC₂ catches up with the host vehicle VC₁ during the execution ofthe relaxation steering control and the inter-vehicle distance isshorter than the determination value LTH, the assistance controldetermination unit 14 determines that the continuity possibility ishigh. When the continuity possibility is determined to be high, theassistance control determination unit 14 does not perform any specialprocessing. Therefore, at the same time when the avoidance steeringcontrol ends at an already set end timing, the return steering controlis started.

Specific Processing in Embodiment 2

FIG. 15 is a flowchart for describing an example of a processing routineimplemented by the driving assistance ECU 10 for realizing the exceptionsteering control according to Embodiment 2. When the processing routineof FIG. 15 is replaced with the processing routine illustrated in FIG. 7, the assistance control processing routine according to Embodiment 2 isdescribed. The processing routine illustrated in FIG. 15 differs fromthe processing routine illustrated in FIG. 7 in that the pieces ofprocessing from step S26 to step S34 are added.

That is, in step S26, when the driving assistance ECU 10 determines thatthe start timing of the avoidance steering control comes, the drivingassistance ECU 10 expands the detection range and adds the detectionrange behind the host vehicle (step S66). The expansion processing andadd processing of the detection range are as described in thedescription of FIG. 14 .

Following step S66, the driving assistance ECU 10 determines presence orabsence of the continuity possibility (step S68). The determinationprocessing relating to the continuity possibility is as described in thedescription of FIG. 14 . When the continuity possibility is determinedto be present, the driving assistance ECU 10 reduces the detection rangein front of the host vehicle and deletes the detection range behind thehost vehicle (step S70). That is, the driving assistance ECU 10 returnsthe detection range expanded in step S68 to the original range.

In step S70, when the continuity possibility is determined to be absent,the driving assistance ECU 10 determines whether the end timing of theavoidance steering control comes (step S72). The processing in step S72is the same as the processing in step S30 of FIG. 7 . When the drivingassistance ECU 10 determines that the end timing of the avoidancesteering control comes, the driving assistance ECU 10 proceeds to stepS70. When the driving assistance ECU 10 determines that the end timingof the avoidance steering control does not come, the driving assistanceECU 10 proceeds to step S34. The pieces of processing after step S34 isas described in FIG. 7 .

With the control device according to Embodiment 2 described above, thefollowing effects can be obtained. That is, when the steering control isselected as the assistance control, the control device not only expandsthe detection range during the execution of the avoidance steeringcontrol but also sets the detection range having the same size as theexpanded detection range behind the host vehicle. Accordingly,appropriateness of the relaxation steering control can be determinedbased on the continuity possibility.

What is claimed is:
 1. A control device for a vehicle, the controldevice comprising: an electronic control unit configured to: executefirst steering control to steer the vehicle in a first direction toavoid a collision with a first object; execute second steering controlto steer the vehicle in a second direction opposite to the firstdirection, following the first steering control; and perform relaxationsteering control to relax the second steering control for avoiding thefirst object when (i) implementation of a next first steering control toavoid a second object is determined to be needed, and (ii) the firstdirection of the first steering control for avoiding the collision withthe first object and a next first direction of the next first steeringcontrol for avoiding the second object are the same.
 2. The controldevice for a vehicle according to claim 1, wherein the electroniccontrol unit is configured to perform the relaxation steering controlbefore starting a next second steering control after the next firststeering control.
 3. The control device for a vehicle according to claim1, wherein: the electronic control unit is configured to set a firstdetection range in front of the vehicle; the electronic control unit isconfigured to set a second detection range behind the vehicle at aposition obtained by rotating the first detection range by 180 degreesaround a center of the vehicle during the execution of the firststeering control such that the electronic control unit detects aparallel traveling vehicle that travels behind the vehicle in a laneadjacent to a lane in which the vehicle travels; the electronic controlunit is configured to determine whether the parallel traveling vehicleapproaches the vehicle during the execution of the relaxation steeringcontrol and whether an inter-vehicle distance between the vehicle andthe parallel traveling vehicle is shorter than a determination valuewhen the parallel traveling vehicle is detected in the second detectionrange during the execution of the first steering control; and theelectronic control unit is configured to perform the second steeringcontrol after the end of the first steering control, when the paralleltraveling vehicle is determined to approach the vehicle during theexecution of the relaxation steering control and the inter-vehicledistance between the vehicle and the parallel traveling vehicle isdetermined to be shorter than the determination value.
 4. The controldevice for a vehicle according to claim 1, wherein: the electroniccontrol unit is configured to, during the execution of the firststeering control, expand the first detection range in a direction infront of the vehicle and in a direction opposite to a movement directionof the vehicle in a right and left direction of the vehicle in the firststeering control; and an expansion width of the first detection range inthe right and left direction is equal to or larger than a movementdistance of the vehicle in the right and left direction in the firststeering control.
 5. The control device for a vehicle according to claim1, wherein: the vehicle includes an external sensor; and the electroniccontrol unit is configured to detect the first object and the secondobject in the first detection range utilizing information acquired bythe external sensor.
 6. A control method of a vehicle including anelectronic control unit, the control method comprising: executing, bythe electronic control unit, first steering control to steer the vehiclein a first direction to avoid a collision with a first object;executing, by the electronic control unit, second steering control tosteer the vehicle in a second direction opposite to the first direction,following the first steering control; and performing, by the electroniccontrol unit, relaxation steering control to relax the second steeringcontrol for avoiding the first object when (i) implementation of a nextfirst steering control to avoid a second object is determined to beneeded, and (ii) the first direction of the first steering control foravoiding the collision with the first object and a next first directionof the next first steering control for avoiding the second object arethe same.